so anywhere you see sulfates indicate that the environment got very dry. here it is. right here was a drought. in calcium, there was an increase here in the '60s. and then you go down. here's another increase in the '30s. it was contemporaneous with our dust bowl period. actually, you know what that is? that's these. thompson: we're now finding that the real story of climate change is not in the science or nature paper that comes from the single site, but it's in the connection, putting these records together, that you see things that you could have never found in one or two sites. narrator: connecting lonnie's tropical ice-core data with cores taken from the polar regions, a record of the earth's temperature and carbon dioxide levels can be established, going back 650,000 years into the past. over this time period, each rise in carbon dioxide levels is accompanied by a rise in temperature. in the most recent period, carbon dioxide levels have been rising to an all-time high. thompson: having that record now that goes back 650,000 years and knowing that co2 in the nat